1. Field of the Invention
The present invention relates to a drying unit coupling apparatus of a liquid electrophotographic printer.
2. Description of the Related Art
In general, a liquid electrophotographic printer such as a color laser printer or copying machine, as shown in FIG. 1, includes a developing unit 20 for developing a predetermined image on a photoreceptor medium 10 such as a photoreceptor web endlessly circulating, a drying unit 30 for drying liquid solution (hereinafter, referred to as carrier) remaining on the developed photoreceptor medium 10, and a transferring unit 40 for transferring the developed image on the photoreceptor medium 10 to a sheet of paper S.
The drying unit 30 includes a drying roller 31 for absorbing the carrier remaining on the photoreceptor medium 10 as drying roller 31 rotates in contact with the photoreceptor medium 10, and heating rollers 32 for vaporizing the carrier absorbed by the drying roller 31 by applying heat.
Here, during printing, the photoreceptor medium 10, the drying roller 31 and the heating rollers 32 are driven in close contact with one another, as shown in the drawing. When driven, the drying roller 31 and the heating rollers 32 absorb and vaporize the carrier, respectively. Meanwhile, when printing is not performed for a long time, the photoreceptor medium 10, the drying roller 31 and the heating rollers 32 need to be separated from one another. Also, in a printing-ready mode before printing begins, it is necessary to preheat the drying roller 31 to save the time needed for it to warm up. For preheating, in the printing-ready mode, the drying roller 31 is separated from the photoreceptor medium 10 and rotated by being in close contact with the heating rollers 32. Thus, in the drying unit 30, the drying roller 31 and the heating roller 32 are allowed to move within a range of a predetermined distance according to a printing mode, a printing-ready mode and a stop mode.
The photoreceptor medium 10 circulates by being wound around a driving roller 12 and rollers 14 and 15, and its surface is uniformly charged by a charger 18. A laser scanning unit 22 scans a laser beam onto the charged photoreceptor medium 10 according to a desired printing image. The surface of the photoreceptor medium 10 is selectively exposed to the scanned laser beam to form an electrostatic latent image. The electrostatic latent image is developed by developer adhering thereto, which is provided by the developing unit 20. The developed developer is squeezed by the developing unit 20 and dried by the drying unit 30, to thus form a desired image. The dried image is transferred to a sheet of paper S via the transferring roller 42 of the transferring unit 40.
However, according to the conventional technology, when the photoreceptor medium 10 or the drying unit 30 needs repairing or replacement, performing repair or replacement is not possible in the state in which the drying roller 31 is separated a predetermined distance from the driving roller 12, that is, in a stop mode. Also, since the drying unit 30 is formed of a single assembly, in order to perform the above works, the entire drying unit 30 must be disassembled and the drying roller 31 detached from the driving roller 12 or a main frame, which inconveniences a user. Accordingly, for the replacement of the photoreceptor medium or the repairing and replacement of the drying unit, more distance between the drying roller 31 and the photoreceptor medium 10 is needed than in a stop mode.
To overcome the above problem, an apparatus for separating a drying unit frame (where the drying roller is installed) a predetermined distance from the main frame (where the driving roller is installed) by using a cam member has been suggested in Korean Patent Application No. 98-44191. In the apparatus, a pair of gears are installed at the main frame and a cam shaft to correspond to each other and be meshed with each other when the main frame and an auxiliary frame, which supports the cam shaft, are coupled to each other. Thus, as the engaged gears rotate, the cam member pushes the drying unit frame in one direction so that the drying unit frame can be separated from or approach the main frame.
In the above apparatus, the gears stay engaged while an operation is performed in each of a stop mode, a printing-ready mode and a printing mode. However, when the engagement of the gears become loose due to movement of the drying unit or if the gears become improperly engaged, the gears may be damaged or an error may occur in the distance that the drying unit is separated from the main frame. Thus, it is necessary to constantly maintain the engagement of the gears when the drying unit is in close contact with the main frame.